While the invention is subject to a wide range of applications, it particularly relates to metal cord, such as that used to reinforce elastomers. More particularly, the present invention is directed to a metallic cord construction used to reinforce rubber articles, including pneumatic tires.
It is known to manufacture metal cords from a plurality of filaments having the same diameter twisted together in the same direction and having the same lay length. The cord is said to have a compact cross-section which is generally the same over the length of the cord. The filaments in the cross-section are arranged in concentric layers in which the filaments are tangential to all the filaments surrounding an individual filament. The single operation produces a cord having a single, compact strand. The single strand, compact cord has the advantages of a reduced cord diameter. These advantages include: (1) a calendared ply having a reduced thickness and, therefore, requiring less calendar rubber; (2) a potential increase in the ends per inch for a given width of ply; and (3) an increased ply strength resulting from an increase in the ends per inch. The uniform cross-section is thought to more uniformly distribute the load carried by the cord to each individual filaments. The result is a higher breaking load. Further, the cord is thought to have improved fatigue resistance and greater flexibility.
In a conventional pneumatic radial tire using metal cords, as described above for reinforcement, the fatigue properties of the carcass ply and belt layer are degraded, mainly by material fatigue due to repeated strain and fretting wear in the contact portion between adjacent filaments. Both of these problems are said to be alleviated by penetration of rubber into the inside of the cord. The rubber layer interposed between the steel filaments is believed to prevent rubbing between adjacent filaments, the so-called "fretting wear."
The present invention relates to a cord having improved rubber penetration into the inside of the cord. The improved rubber penetration will also provide the cord with higher corrosion resistance should the cord be exposed to moisture.